No wonder good steak is hard to find: it's going extinct, along with the elderly cattle it comes from. For years I have been chasing down the secret to the ultimate steak, and I had reason to believe it lay somewhere in northern Spain. So Madrid-based food writer Pedro Espinosa agreed to meet me deep in the Basque hills surrounding San Sebastián, from where we would eat our way cross-country to El Capricho, a restaurant near the tiny town of Jiménez de Jamuz in the northwestern province of León. We knew that José Gordón Ferrero, the restaurant's beef-obsessed owner, had been...